Rotary lawn mowers have become standard equipment for homeowners who wish to trim and maintain their lawns. Such mowers typically have an internal combustion engine mounted on an engine shroud or housing. The engine turns a rotatable metal cutting blade underneath the engine shroud. The sharpened edges of such blades become dull rather quickly and it becomes necessary to frequently replace or sharpen the blade.
Sharpening the blade edges while the blade is attached to the mower is a difficult and hazardous task, as is well known by anyone who has tried it. For example, it is difficult to keep the blade from turning on its axis while trying to sharpen the edges. Further, the rotating blade can easily spin and injure a hand or foot during the process.
Hence, it is preferable to remove the blade from the mower for sharpening. But this task can be difficult and hazardous too. Generally, conventional cutting blades are attached to the rotary drive means of the mower with one or more metal bolts. These bolts tend to corrode and to become encrusted with dirt, grease and dried grass clippings after considerable use, and removing these bolts can be very difficult and time consuming. Such removal can also be hazardous because when attempting to loosen the bolts, the blade tends to rotate and care must be taken to avoid injury to a hand or foot. Once the blade has been removed and sharpened, however, reattachment has the same problems.
Quick-release or detachable blades have been the goal of innovators in this art for some time. For example, U.S. Pat. No. 3,877,146 (issued Apr. 15, 1975 to Pittinger) relates to a plastic holder for blades in rotary grass trimmers, fans or similar apparatus. The holder is designed to releasably hold the blade with elastically deformable retaining portions or plastic fingers. Although this plastic holder may be suitable for small rotary grass trimmers or fans, it would not be useful in heavy-duty cutting equipment, such as rotary lawn mowers. The plastic blade is held in the holder merely by two deformable plastic fingers which would very likely be deformed and release the blade if it struck a rock or other hard object during use. If the blade was prematurely released or broken, the flying parts would be highly dangerous to the user or bystanders. Hence, this plastic apparatus has limited utility and safety features.
Therefore, it would be desirable to have a holder for securely retaining a cutting blade, but from which holder the blade can be easily and safely released for sharpening or replacement.